All the purity percentages are molar percentages.
From WO-A-06/054008 it is known how to produce carbon dioxide from a PSA tail by treating a gas from a reverse conversion.
The main steps in the ammonia synthesis are:
1. steam reforming natural gas (or another carbon-containing fuel).
2. second reforming/partial oxidation in air, to add nitrogen for the ammonia synthesis reaction.
3. reacting CO into CO2 and H2 on a catalyst.
4. extracting CO2 by washing with a solvent (aMDEA®, Benfield method, etc.).
5. methanating traces of CO and CO2 into CH4 and H2O on a catalyst using a high hydrogen excess (CO and CO2 being poisons for the catalyst).
6. ammonia synthesis with two possible variants:
a. dry+wash with nitrogen to adjust the H2/N2 ratio to 3 and extract surplus CH4, argon and N2+NH3 synthesis loop via catalytic reactors,
b. or: NH3 synthesis loop via catalytic reactors+treat the purge evacuating CH4, argon and excess N2 on a PSA to recover the H2.
When there is a desire to further use the CO2 extracted in step 4 (for example to make oil extraction easier or to produce a chemical such as urea, etc.) or if there is a desire to sequester it to reduce greenhouse gas emissions, a compression and drying step for the CO2 extracted in step 4 must be added.
The invention proposed aims to significantly reduce the cost of NH3 production when the CO2 must be compressed to be further used as described above.
Therefore there is a need for an economically viable method for producing ammonia synthesis gas and carbon dioxide.